An olefin (e.g., alkene) is an unsaturated hydrocarbon containing one or more pairs of carbon atoms linked by a double bond. Olefins are classified in either or both of the following ways: (1) as cyclic or acyclic (aliphatic) olefins, in that the double bond is located between carbon atoms forming part of a cyclic (closed-ring) or of an open-chain grouping, respectively, and (2) as monoolefins, diolefins, triolefins, etc., in that the number of double bonds per molecule is, respectively, one, two, three, or some other number. Olefins containing two to four carbon atoms per molecule are gaseous at ordinary temperatures and pressures; those containing five or more carbon atoms are usually liquid at ordinary temperatures and pressures. Oxidation of an olefin occurs when the functional group (e.g., double carbon-carbon bond) is broken (e.g., cracked) to allow an oxygen molecule to attach to the hydrocarbon.
Oxidized olefins are used in many chemical processes. For example, ethylene oxide is an important raw material in many large scale chemical productions, such as ethylene glycols, ethylene glycol ethers, and ethoxylates. Ethylene glycol and the other derivatives produced from the oxidized olefin ethylene oxide can be found in antifreeze, in the production of polyester, and polyethylene terephthalate, liquid coolants and solvents, perfumes, cosmetics, pharmaceuticals, lubricants, paint thinners, and plasticizers. Ethylene glycol ethers are part of brake fluids, detergents, solvents, lacquers, and paints. Ethoxylates are reaction products of ethylene oxide with higher alcohols, acids or amines. They are used in the manufacture of detergents, surfactants, emulsifiers, and dispersants.
The production of oxidized olefins via direct oxidation is generally known. The oxidation involves catalytic oxidation of an olefin with oxygen over a catalyst to yield an oxidized olefin. Generally, the process can be divided into two processes depending on the source of the oxidizing agent—the air-based process and the oxygen based process. In the first, air or air enriched with oxygen is fed directly to the system. In the second, a high purity oxygen stream (e.g., greater than 98 mol %) from an air separation unit is employed as the source of the oxidizing agent.
Normally the reaction vessel and the oxidized olefin product are cooled to prevent further reaction of the oxidized olefin (e.g., isomerisation). Failure to cool the oxidized olefin product could result in further reactions that could render undesired byproducts. Further, reaction vessel temperature control is a concern, as the oxidation of olefins is a highly exothermic reaction and without proper temperature control mechanisms could result in a “runaway reaction.” Typically the reaction vessel temperature can be controlled via a coolant circulating through the reaction vessel, controlling the promoter concentration, or both.